This invention relates to an aqueous pigment ink composition suitable for use in inkjet recording and more particularly, to an aqueous pigment ink composition which keeps stable dispersion of the pigment and which can be printed on any recording material to form printed images having rub-off resistance and water fastness.
Since conventional dye base inks commonly used in the inkjet recording technology undesirably lack light fastness and water fastness, pigment base inks featuring superior water fastness and light fastness are now used in part. Especially as to black ink, carbon black pigment ink has substituted for the dye base ink.
Since aqueous pigment ink uses inorganic pigment particles having good water fastness and light-fastness in themselves as the colorant, images printed on an object therewith are improved in water fastness and light-fastness over the dye base ink. However, since the pigment ink is not dissolved in water as is the dye ink, essentially the pigment ink merely rests on the object to be recorded. Then when the pigment ink is printed on the object to be recorded, typically a sheet of plain paper, the printed image is less resistant to water and removed by rubbing. On use of a marker filled with the pigment ink, images marked therewith are blurred or stained. An attempt would be made to add a binder to the pigment ink to bind pigment particles. Since the aqueous pigment ink is a dispersion of essentially water-insoluble pigment particles in water with the aid of a dispersant or the like, the addition of the binder can cause the particles to flocculate, exacerbating storage stability and often causing the inkjet head to be clogged.
An object of the invention is to provide a novel and improved pigment ink composition which is suited for use in the aqueous ink recording technology, especially the inkjet recording technology, forms printed images having rub-off resistance and water fastness, and has storage stability.
We have found that a pigment ink composition obtained by formulating in a specific proportion (I) an inorganic pigment, (II) an organosilicon compound (C) obtained by hydrolysis of (A) 100 parts by weight of a hydrolyzable silane containing an amino group-bearing organic group represented by the following general formula (1) or a partial hydrolyzate thereof and (B) 5 to 200 parts by weight of a hydrolyzable silane represented by the following general formula (2) or a partial hydrolyzate thereof, and (III) water is suited for use in the aqueous ink recording technology, especially the inkjet recording technology. When the pigment ink composition is printed on an object to be recorded, the printed images is bound to the object and have rub-off resistance and water fastness. Additionally, the composition remains stable during storage.
YR1mSiR23xe2x88x92mxe2x80x83xe2x80x83(1)
Herein R1 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R2 is an alkoxy or acyloxy group of 1 to 4 carbon atoms, Y is an amino group-bearing organic group, and m is equal to 0 or 1.
R3nSiR44xe2x88x92nxe2x80x83xe2x80x83(2)
Herein R3 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R4 is an alkoxy or acyloxy group of 1 to 4 carbon atoms, and n is equal to 0, 1 or 2.
Accordingly, the invention provides a pigment ink composition comprising (I) 10 parts by weight of the inorganic pigment, (II) 0.001 to 10 parts by weight of the above-mentioned organosilicon compound (C), and (III) 10 to 10,000 parts by weight of water.
Component (I) of the pigment ink composition according to the invention is an inorganic pigment which is typically selected from carbon black, titanium oxide, and iron oxide, but not limited thereto. Of these, carbon black is preferred. These inorganic pigments may be used as such although inorganic pigments are preferably surface modified with an organic substance adsorbing or bonding to the surface, for enhancing the dispersion and stability thereof in a medium. For example, a pigment is treated with an organoalkoxysilane for enhancing the dispersion with the aid of a dispersant as described in JP-A 11-61012. Carbon black particles are surface modified by graft polymerization from polymerization initiator groups that are introduced to particle surfaces on the basis of carboxyl or phenolic hydroxyl groups on particle surfaces as described in Carbon, No. 140, 322 (1989) and Surface, No. 28, 286 (1990).
Component (II) is an organosilicon compound (C) which serves to bind the pigment component in the pigment ink composition to an object to be recorded. This component is effective only in a minor amount and does not adversely affect the storage stability of the pigment ink composition.
The organosilicon compound (C) is obtained by hydrolysis of (A) a hydrolyzable silane containing an amino group-bearing organic group represented by the following general formula (1):
YR1mSiR23xe2x88x92mxe2x80x83xe2x80x83(1)
wherein R1 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R2 is an alkoxy or acyloxy group of 1 to 4 carbon atoms, Y is an amino group-bearing organic group, and m is equal to 0 or 1, or a partial hydrolyzate thereof, and (B) a hydrolyzable silane represented by the following general formula (2):
R3nSiR44xe2x88x92nxe2x80x83xe2x80x83(2)
wherein R3 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R4 is an alkoxy or acyloxy group of 1 to 4 carbon atoms, and n is equal to 0, 1 or 2, or a partial hydrolyzate thereof.
The hydrolyzable silane containing an amino group-bearing organic group represented by formula (1) is a component for rendering the system soluble in water, that is, for endowing the end organosilicon compound (C) with water solubility. The hydrolyzable silanes may be used alone or in admixture of two or more while partial hydrolyzates thereof are also useful.
YR1mSiR23xe2x88x92mxe2x80x83xe2x80x83(1)
In formula (1), R1 represents substituted or unsubstituted monovalent hydrocarbon groups of 1 to 8 carbon atoms, for example, unsubstituted monovalent hydrocarbon groups such as alkyl, alkenyl, aryl and aralkyl groups, and substituted monovalent hydrocarbon groups in which some or all of the hydrogen atoms on the foregoing groups are replaced by halogen atoms or the like, such as halogenated alkyl groups. Illustrative, non-limiting, examples include xe2x80x94CH3, xe2x80x94CH2CH3, xe2x80x94CH2CH2CH3, xe2x80x94CH(CH3)2, xe2x80x94CH2CH2CH2CH3, xe2x80x94CH(CH3)CH2CH3, xe2x80x94CH2CH(CH3)CH3, xe2x80x94C(CH3)3, xe2x80x94C6H5, and xe2x80x94C6H13.
R2 represents alkoxy or acyloxy groups of 1 to 4 carbon atoms. Illustrative, non-limiting, examples include xe2x80x94OCH3, xe2x80x94OCH2CH3, xe2x80x94OCH2CH2CH3, xe2x80x94OCH(CH3)2, xe2x80x94OCH2CH2CH2CH3, xe2x80x94OCH(CH3)CH2CH3, xe2x80x94OCH2CH(CH3)CH3, xe2x80x94OC(CH3)3, xe2x80x94OCOCH3, and xe2x80x94OCOCH2CH3.
Y is an amino group-bearing organic group. For example, it is represented by the following formula (3). 
Herein, R5 and R6 represent hydrogen or monovalent hydrocarbon groups of 1 to 8 carbon atoms, and they may be the same or different. R7 and R8 represent divalent hydrocarbon groups of 1 to 8 carbon atoms, and they may be the same or different. The letter p is 0 or an integer of 1 to 3. It is noted that the monovalent hydrocarbon groups of 1 to 8 carbon atoms are the same as described above for R1; and alkylene groups are exemplary of the divalent hydrocarbon groups of 1 to 8 carbon atoms.
Illustrative, non-limiting, examples of the amino group-bearing organic group represented by Y are given below.
H2NCH2xe2x80x94, H(CH3)NCH2xe2x80x94, H2NCH2CH2xe2x80x94, H(CH3)NCH2CH2xe2x80x94H2NCH2CH2CH2xe2x80x94, H(CH3)NCH2CH2CH2xe2x80x94, (CH3)2NCH2CH2CH2xe2x80x94, H2NCH2CH2NHCH2xe2x80x94, H(CH3)NCH2CH2NHCH2CH2CH2xe2x80x94, (CH3)2NCH2CH2NHCH2CH2CH2xe2x80x94, H2NCH2CH2NHCH2CH2NHCH2CH2CH2xe2x80x94, H(CH3)NCH2CH2NHCH2CH2NHCH2CH2CH2xe2x80x94.
Of these, H2NCH2CH2CH2xe2x80x94, H2NCH2CH2NHCH2CH2CH2xe2x80x94 and H2NCH2CH2NHCH2CH2NHCH2CH2CH2xe2x80x94 are preferred.
The letter m is equal to 0 or 1.
Illustrative, non-limiting, examples of the hydrolyzable silane containing an amino group-bearing organic group (A) are given below.
H2NCH2Si(OCH3)3, H2NCH2Si(OCH2CH3)3, H2NCH2SiCH3(OCH3)2, H2NCH2SiCH3(OCH2CH3)2, H2NCH2CH2Si(OCH3)3, H2NCH2CH2Si(OCH2CH3)3, H2NCH2CH2SiCH3(OCH3)2, H2NCH2CH2SiCH3(OCH2CH3)2, H2NCH2CH2CH2Si(OCH3)3, H2NCH2CH2CH2Si(OCH2CH3)3, H2NCH2CH2CH2SiCH3(OCH3)2, H2NCH2CH2CH2SiCH3(OCH2CH3)2, H(CH3)NCH2CH2CH2Si(OCH3)3, H(CH3)NCH2CH2CH2Si(OCH2CH3)3, H(CH3)NCH2CH2CH2SiCH3(OCH3)2, H(CH3)NCH2CH2CH2SiCH3)OCH2CH3)2, H2NCH2CH2NHCH2CH2CH2Si(OCH3)3, H2NCH2CH2NHCH2CH2CH2Si(OCH2CH3)3, H2NCH2CH2NCH2CH2CH2SiCH3(OCH3)2, H2NCH2CH2NHCH2CH2CH2SiCH3(OCH2CH3)2, H(CH3)NCH2CH2NHCH2CH2CH2Si(OCH3)3, H(CH3)NCH2CH2NHCH2CH2CH2Si(OCH2CH3)3, H(CH3)NCH2CH2NHCH2CH2CH2SiCH3(OCH3)2, H(CH3)NCH2CH2NHCH2CH2CH2SiCH3(OCH2CH3)2, H2NCH2CH2NHCH2CH2NHCH2CH2CH2Si(OCH3)3, H2NCH2CH2NHCH2CH2NHCH2CH2CH2Si(OCH2CH3)3, H2NCH2CH2NHCH2CH2NHCH2CH2CH2SiCH3(OCH3)2, H2NCH2CH2NHCH2CH2NHCH2CH2CH2SiCH3(OCH2CH3)2 
Of these, the following compounds are especially preferred.
H2NCH2CH2NHCH2CH2CH2Si(OCH3)3, H2NCH2CH2NHCH2CH2CH2Si(OCH2CH3)3
The other hydrolyzable silane (B) to be used in admixture with the hydrolyzable silane containing an amino group-bearing organic group or its partial hydrolyzate (A) is represented by the following general formula (2). The other hydrolyzable silanes may also be used alone or in admixture of two or more while partial hydrolyzates thereof are also useful.
R3nSiR44xe2x88x92nxe2x80x83xe2x80x83(2)
In formula (2), R3 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R4 is an alkoxy or acyloxy group of 1 to 4 carbon atoms, and n is equal to 0, 1 or 2.
The substituted or unsubstituted monovalent hydrocarbon groups of 1 to 8 carbon atoms represented by R3 are the same as described above for R1. Illustrative, non-limiting, examples include xe2x80x94CH3, xe2x80x94CH2CH3, xe2x80x94CH2CH2CH3, xe2x80x94CH(CH3)2, xe2x80x94CH2CH2CH2CH3, xe2x80x94CH(CH3)CH2CH3, xe2x80x94CH2CH(CH3)CH3, xe2x80x94C(CH3)3, xe2x80x94C6H5, and xe2x80x94C6H13.
R4 represents alkoxy or acyloxy groups of 1 to 4 carbon atoms. Illustrative, non-limiting, examples include xe2x80x94OCH3, xe2x80x94OCH2CH3, xe2x80x94OCH2CH2CH3, xe2x80x94OCH(CH3)2, xe2x80x94OCH2CH2CH2CH3, xe2x80x94OCH(CH3)CH2CH3, xe2x80x94OCH2CH(CH3)CH3, xe2x80x94OC(CH3)3, xe2x80x94OCOCH3, and xe2x80x94OCOCH2CH3.
Illustrative, non-limiting, examples of the hydrolyzable silane (B) are given below.
Si(OCH3)4, Si(OCH2CH3)4, Si(OCH2CH2CH3)4, Si(OCH2CH2CH2CH3)4, CH3Si(OCH3)3, CH3Si(OCH2CH3)3, CH3Si(OCH2CH2CH3)3, CH3Si(OCH2CH2CH2CH3)3, (CH3)2CHSi(OCH3)3, (CH3)2Si(OCH3)2, (CH3)2Si(OCH2CH3)2, (CH3)2Si(OCCH2CH2CH3)2, (CH3)2Si(OCH2CH2CH3)2, ((CH3)2CH)2Si(OCH3)2, 
Of these, Si(OCH3)4, Si(OCH2CH3)4, CH3Si(OCH3)3, CH3Si(OCH2CH3)3, (CH3)2Si(OCH3)2 and (CH3)2Si(OCH2CH3)2 and partial hydrolyzates thereof are especially preferred.
Upon hydrolysis, 5 to 200 parts by weight, preferably 10 to 150 parts by weight of the hydrolyzable silane or partial hydrolyzate (B) is mixed with 100 parts by weight of 25 the hydrolyzable silane or partial hydrolyzate (A). More than 200 parts of component (B) on this basis is undesirable because the dispersion stability of the pigment is exacerbated.
In producing the organosilicon compound (C) as 30 component (II), water is mainly used as the solvent. If necessary, an organic solvent soluble in water such as an alcohol, ester, ketone or glycol is used in admixture with water. Such organic solvents include alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol and 2-propyl alcohol, esters such as methyl acetate, ethyl acetate and ethyl acetoacetate, ketones such as acetone and methyl ethyl 5 ketone, and glycols such as glycerin and diethylene glycol.
An appropriate amount of the solvent is about 400 to 5,000 parts by weight and more preferably about 1,000 to 3,000 parts by weight per 100 parts by weight of the starting silanes combined. Less than 400 parts of the 10 solvent may allow hydrolysis reaction to proceed beyond the desired extent, resulting in a non-uniform system or storage instability. More than 5,000 parts of the solvent is uneconomical in some cases.
The amount of water in the solvent is preferably 15 adjusted such that the molar ratio of water to the starting silanes may fall in the range of 5/1 to 50/1. If this molar ratio is less than 5, hydrolysis may not proceed to the completion, sometimes resulting in an unstable liquid. A molar ratio in excess of 50 may invite an economical 20 disadvantage.
Hydrolysis may be effected by any of the following reaction procedures (1) to (4). Procedure (1) is to add dropwise a mixture of silanes (A) and (B) to water or a mixture of an organic solvent and at least a necessary 25 amount of water to effect hydrolysis. Procedure (2) is to add dropwise water to a mixture of silanes (A) and (B) or a mixture of silanes (A) and (B) and an organic solvent. In procedure (3), the hydrolyzable silane or partial hydrolyzate (B) is added dropwise to water or a mixture of 30 an organic solvent and at least a necessary amount of water to effect hydrolysis, followed by dropwise addition of the hydrolyzable silane or partial hydrolyzate (A). In procedure (4), the hydrolyzable silane or partial hydrolyzate (A) is added dropwise to water or a mixture of 35 an organic solvent and at least a necessary amount of water to effect hydrolysis, followed by dropwise addition of the hydrolyzable silane or partial hydrolyzate (B). Of these, reaction procedure (1) is especially preferred from the standpoint of stability of a water-fast ink composition.
It is understood that the organosilicon compound (C) is obtained in the form of an aqueous solution. If necessary, by further adding or removing water, the solution is adjusted to a solution containing 10 to 2,000 parts by weight of water per 100 parts by weight of the organosilicon compound (C).
The thus obtained component (II) remains stable in an aqueous ink composition during storage, and especially does not alter the dispersed state of the pigment (I) therein and keeps the pigment in stable dispersion, and enables to firmly bind the pigment to the object to be recorded.
An appropriate amount of component (II) added, which varies with a particular type of pigment (I), is usually 0.001 to 10 parts, and especially 0.01 to 3 parts by weight of the organosilicon compound (C), which is an active constituent of component (II), per 10 parts by weight of pigment (I). Less than 0.001 part of the organosilicon compound (C) is less effective whereas more than 10 parts achieves no further effect and rather adversely affects the dispersion stability of the liquid ink composition.
Component (III) is water serving as a solvent for the water-fast ink composition. An appropriate amount of water is 10 to 10,000 parts by weight per 10 parts by weight of pigment (I). Less than 10 parts of water adversely affects the storage stability of the water-fast ink composition. An ink composition containing more than 10,000 parts of water is too dilute to form images when printed.
It is advantageous to add a humectant to the pigment ink composition which is used in the inkjet recording method because the humectant is effective for precluding nozzle clogging and enhancing ink discharge stability. Useful humectants are polyhydric alcohols. Glycerin, diethylene glycol, triethylene glycol, low molecular weight polyethylene glycol and polyvinyl alcohols are exemplary though the humectant is not limited thereto. A mixture of two or more of these humectants is also employable.
An appropriate amount of the humectant added is about 1 to 40 parts, and especially about 5 to 30 parts by weight per 10 parts by weight of the pigment (I). Less than 1 part of the humectant is ineffective for improving ink discharge stability. More than 40 parts of the humectant may weaken the binding of the pigment and is uneconomical in some cases.
For imparting any other desirable properties to the water-fast ink composition, other additives are optionally added insofar as the stability and other advantages are not impaired. Such optional additives include dispersants, UV absorbers, anti-foaming agents, and surfactants. Also, microparticulate inorganic oxides or sol thereof, water-soluble polymers or the like may be added for reinforcement purposes.
The pigment ink composition of the invention has satisfactory storage or dispersion stability and discharge stability and forms printed images having rub-off resistance and water fastness.